For safety, the power supplying side of a conductive couple is generally the female part, and does not have bare conductive elements protruding therefrom. A plug coupled to the device is the corresponding male part with bare pins. The size of the pins and holes are such that a child cannot insert his or her fingers thereinto. In high quality sockets, an earth connection is provided, and, only when a plug with a longer earth pin is inserted thereinto, is it possible to insert a pin (or anything else) into the holes connected to the current carrying live and neutral wires. Nevertheless, socket holes are dangerous and children do sometimes manage to insert pencils, pins and other objects into socket holes, sometimes with fatal results. Water can also cause shorting and may result in electrocution.
It can therefore be safer and more reliable to provide socket-less power outlets such as inductive couplers. Inductive power coupling allows energy to be transferred from a power supply to an electric load without connecting wires. A power supply is wired to a primary coil and an oscillating electric potential is applied across the primary coil which induces an oscillating magnetic field therearound. The oscillating magnetic field may induce an oscillating electrical current in a secondary coil, placed close to the primary coil. In this way, electrical energy may be transmitted from the primary coil to the secondary coil by electromagnetic induction without the two coils being conductively connected. When electrical energy is transferred inductively from a primary coil to a secondary coil, the pair are said to be inductively coupled. An electric load wired in series with such a secondary coil may draw energy from the power source when the secondary coil is inductively coupled to the primary coil.
Low power inductive electrical power transmission systems over extended surfaces are not new. One such example is described in U.S. Pat. No. 7,164,255 to Hui. In Hui's system a planar inductive battery charging system is designed to enable electronic devices to be recharged. The system includes a planar charging module having a charging surface on which a device to be recharged is placed. Within the charging module, and parallel to the charging surface, at least one, and preferably an array of primary windings are provided. These couple energy inductively to a secondary winding formed in the device to be recharged. Such systems are adequate for charging batteries in that they typically provide a relatively low power inductive coupling. It will be appreciated however, that extended base units such as Hui's charging surface which transmit energy continually approximately uniformly over the whole area of the unit, are not suitable for use with high energy systems.
By not requiring holes for coupling pins, socket-less outlets may be disguised more effectively than conductive sockets, and are thus less obtrusive. A primary inductive coil, for example, may be concealed behind a surface. Generally, the fact that socket-less outlets are less obtrusive is advantageous. But being harder to spot than conventional power outlets has its disadvantages. The user must somehow locate the outlet before being able to use it by bringing a secondary coil into proximity therewith. The problem of locating such sockets is particularly acute where the power outlets are behind a concealing surface such as a desk top or wall, and the positions thereof are adjustable over a large area.
Locating mobile source ‘hotspots’ or sockets is particularly problematic in high power systems where no extended power transmission surface is provided. Moreover, a high power primary coil produces a large oscillating magnetic field. Where a secondary coil is inductively coupled to the primary coil, the resulting flux linkage causes power to be drawn into the secondary coil. Where there is no secondary coil to focus the power, the oscillating magnetic field causes high energy electromagnetic waves to be transmitted which may be harmful to bystanders. In contrast to low power systems, such as Hui's charging surface, where excess heat may be readily dissipated, uncoupled high power primary coils and their surroundings may become dangerously hot.
In order to provide power to electrical devices in an efficient manner it is important that certain parameters of the power are regulated. By feeding back such parameters as working voltage, current, temperature and the like, the power supply to an electric device may be optimized to minimize energy losses and to prevent excessive heating of the components. Consequently, it may be useful to provide a signal transfer channel for power regulation and the like. Thus a communication channel between source and load device is often provided alongside the power input channel in conventional conductive power supply systems. Methods for providing such a communication channel include wired connections to the device that are often packaged in the same cable as the power lines and conductively coupled to the load via conventional pin-and-socket type connectors.
Leak prevention systems which are able to detect power emanating from a primary coil of an inductive power source and to cut off power to the primary coil if no secondary coil is coupled thereto have been considered. However in order to prevent power leakage from a primary coil while a secondary coil is coupled thereto, a communication channel between the secondary and primary coil would be useful. Nevertheless due to the lack of connecting wires in inductive power couplings, conductive communication channels are not practical.
There is a need for a control system for inductive power outlets, which is capable of locating a concealed power outlet, preventing power leakage from the power outlet, locating secondary coils close to the power outlet and regulating power transfer from the power outlet to a secondary coil coupled thereto. The present invention addresses this need.